Appendix 13
Modelling Foot-and-Mouth disease: A comparison of epidemiological models François MOUTOU, Benoît DURAND AFSSA, LERPAZ, Epidemiology Unit, BP 67, 94703 Maisons-Alfort cedex, France Tel : 33 1 49 77 13 33, fax : 33 1 43 68 97 62, E mail : f.moutou@alfort.afssa.fr
Introduction Models have been used for some times with the aim of helping in decision making around Foot-and-Mouth Disease (FMD) outbreaks. However, up to very recently, most of these models could mainly be seen as training tools, because Western European and North American countries, as well as Australia and New Zealand, where many of them have been developed, had been free of FMD for many years, or even never experienced the disease like New Zealand. In fact, most of the data used were those collected during the 1967-1968 UK epizootics, under farming conditions certainly different from those prevailing today. More recently, with the sanitary measures –ban on vaccination– implemented over Europe, a new demand arose. However, most of the models were still used either as tools to better understand FMD virus transmission including airborne transmission, to mimic an outbreak, for training purposes, or to compare economical scenarios. The 2001 epizootics, bringing a lot of new data about FMD transmission under today farming conditions, was the occasion for new modelling. In the UK, during 2001, different models were run and published, with conclusions used to control the disease by the authorities. Here we try to present and to compare these models, from what has been published. What is modelling? Modelling is by no means a new tool in epidemiology, even if the development of smaller but much more powerful and easier to use computers -and software- certainly helped a lot. If modelling is aimed at a better understanding of reality and is seen as an instrument in decision making, it more often pinpoints where data are lacking or where understanding of a natural phenomenon is still to be improved. Modelling in epidemiology cannot be seen without a strong connection with field data, even if it should be able to bring help to take decision when not everything is known, a classical situation. FMD is a good example of a disease that can be computed, at least in our west European farming conditions, due to: -fast spreading of the virus through airborne route to four domestic species, -officially good agricultural statistics, -knowledge of animal movements, -the absence, up to now, of wild reservoirs or vectors. During the spring of 2001, different teams made projections, from the beginning of the epizootics, to predict its probable size and duration. A recent synthesis already compared these results (Kao 2002). The present paper will use this reference at large.
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